Shoe sole member

ABSTRACT

The invention aims to provide a shoe sole member capable of achieving comfort when using shoes and exhibiting excellent shape-recovering properties after using the shoes. Provided is a shoe sole member formed using a polymer foam, and the polymer foam contains fibers dispersed therein.

FIELD

The present invention relates to a shoe sole member. More specifically,the present invention relates to a shoe sole member that is used, forexample, as an inner sole, a sock liner, a midsole, or an outer sole.

BACKGROUND

Conventionally, polymer foams formed by foaming a composition whose maincomponent is a polymer such as resins and rubbers are used for variousapplications because of their excellent cushioning properties, and arewidely used also for sporting goods. Sports shoes used for variouscompetitions are composed of various members. For example, a shoe soleis composed of shoe sole members such as an outer sole, a midsole, andan inner sole. Such a shoe sole member is formed using a polymer foamwhose main component is a crosslinked resin since it is required to haveproperties such as light weight, mechanical strength to suppressdeformation due to a long-term use and to withstand severe useconditions, and shock absorbing properties.

As polymer foams used for shoe sole members, polymer foams formed bycrosslinking and foaming polyurethane, natural rubber, or ethylene-vinylacetate copolymer are conventionally known. Particularly, a polymer foamformed by crosslinking and foaming a polymer composition whose maincomponent is ethylene-vinyl acetate copolymer is suitable for use as ashoe sole member from the viewpoint of durability and cost (see PatentLiterature 1 below).

However, such a conventional polymer foam has a problem that, whencompressive strain is applied for a long time, it is difficult torecover its shape as before, which phenomenon is significantparticularly when the polymer foam is highly foamed. Therefore, there isa fear that the compressive deformation of the conventional shoe solemember applied in use does not sufficiently recover after use, in thecase where a polymer foam that is highly foamed more than conventionalfoaming is employed as a forming material in efforts to obtainlightweight properties. A shoe sole member having excellent recoveringproperties from the compressive deformation can be obtained generally byemploying a foam product formed using a resin having high rigidity as aforming material. However, the hardness of the foam product formed usinga resin having high rigidity tends to increase beyond a necessaryhardness as a shoe sole member, as compared to a foam product formedusing a soft resin having low rigidity, which makes it difficult tosufficiently give comfort when using shoes.

That is, the conventional shoe sole member has a problem that excellentshape-recovering properties after using the shoes are difficult toachieve, in order to achieve comfort when using shoes.

CITATION LIST Patent Literature

Patent Literature 1: JP H11-206406 Å

SUMMARY Technical Problem

In order to solve the aforementioned problem, it is an object of thepresent invention to provide a shoe sole member capable of achievingcomfort when using shoes and exhibiting excellent shape-recoveringproperties after using the shoes.

Solution to Problem

As a result of diligent studies in order to solve the aforementionedproblem, the inventor has found that properties such as compression setcan be significantly improved by dispersing fibers in a polymer foamwithout excessively increasing the hardness of the polymer foam. Thus,the present invention has been accomplished. That is, in order to solvethe aforementioned problem, the present invention relating to a shoesole member is characterized in that the shoe sole member is partiallyor entirely formed using a polymer foam that is formed by foaming apolymer composition, and the polymer foam contains fibers dispersedtherein.

Advantageous Effects of Invention

Shoe sole members undergo compressive deformation due to the weight of awearer when using shoes. In the polymer foam used for the shoe solemember of the present invention, fibers are dispersed, and thereforestresses such as bending stress and tensile stress are allowed to act onthe fibers upon the compressive deformation of the polymer foam.Accordingly, the recovery force of the fibers against the bending stressand the tensile strength of the fibers against the tensile stress can beutilized for recovering the shape of the polymer foam after using theshoes.

Thus, the present invention can give comfort during use to the shoe solemember formed using the polymer foam and excellent recovering propertiesafter the use from deformation applied during the use.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a substantial side view showing an aspect of a shoe solemember.

FIG. 2 is an image of a scanning electron microscope (SEM) as a resultof cross sectional observation of a polymer foam in which fibers aredispersed.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of a shoe sole member of the present inventionare described, for example. FIG. 1 shows a shoe formed using the shoesole member of this embodiment. A shoe 1 has an upper material 2 andshoe sole members 3 and 4. The shoe 1 has a midsole 3 and an outer sole4 as shoe sole members. The shoe sole members are formed using a polymerfoam in which fibers are dispersed. The shoe sole members of thisembodiment, for example, can be formed using the polymer foam having aspecific gravity of not more than 0.15 and a compression set of not morethan 40%.

The polymer foam in this embodiment has a specific gravity of not morethan 0.15, in order to give excellent lightweight properties to the shoesole members. The polymer foam preferably has a specific gravity of atleast 0.01, more preferably at least 0.05. The specific gravity of thepolymer foam means a value measured by “underwater displacement”prescribed in JIS K7112 as the method A under a temperature condition of23° C. The specific gravity can be measured using a hydrometer having amechanism to prevent floating of samples, and can be measured, forexample, using a commercially available hydrometer from Alfa Mirage Co.,Ltd., as a high-precision electronic hydrometer.

If the shoe sole members are formed using a polymer foam having anexcessively low hardness, the foot comfort of shoes including the shoesole members may possibly be reduced. Therefore, the Asker C hardness ofthe polymer foam is preferably at least 10 and not more than 80, morepreferably at least 20 and not more than 70. The Asker C hardness of thepolymer foam means an instantaneous value obtained by performing aspring hardness test prescribed in JIS K7312 as the type Cat 23° C.

In this embodiment, the compression set of the polymer foam is not morethan 40%, in order to allow the shoe sole members subjected tocompressive deformation when using shoes to easily recover after usingthe shoes to the state before the use. Since it is not easy tocompletely eliminate the compression set of the polymer foam, thecompression set of the polymer foam is preferably at least 1%, in orderto facilitate the production of the shoe sole members. The compressionset herein means a value measured based on the method A in ASTM D395(constant load test), and is a value obtained by applying a pressure of0.59 MPa to a measurement sample for 22 hours under a temperaturecondition of 23° C., and measuring the thickness of the measurementsample after a lapse of 24 hours after the measurement sample isreleased from the pressure.

The polymer composition constituting the polymer foam may be crosslinkedor uncrosslinked. However, in order to exhibit such properties of thecompression set as mentioned above, it is preferable that the polymercomposition constituting the polymer foam is crosslinked. In thisembodiment, the base polymer that is the main component of the polymercomposition is not specifically limited, and may be the same as polymersconventionally used for forming shoe sole members.

Examples of the base polymer include polyethylene, polypropylene,ethylene-propylene copolymer, propylene-1-hexene copolymer,propylene-4-methyl-1-pentene copolymer, propylene-1-butene copolymer,ethylene-1-hexene copolymer, ethylene-4-methyl-pentene copolymer,ethylene-1-butene copolymer, 1-butene-1-hexene copolymer,1-butene-4-methyl-pentene, ethylene-methacrylic acid copolymer,ethylene-methyl methacrylate copolymer, ethylene-ethyl methacrylatecopolymer, ethylene-butyl methacrylate copolymer, ethylene-methylacrylate copolymer, ethylene-ethyl acrylate copolymer, ethylene-butylacrylate copolymer, propylene-methacrylic acid copolymer,propylene-methyl methacrylate copolymer, propylene-ethyl methacrylatecopolymer, propylene-butyl methacrylate copolymer, propylene-methylacrylate copolymer, propylene-ethyl acrylate copolymer, propylene-butylacrylate copolymer, ethylene-vinyl acetate copolymer, andpropylene-vinyl acetate copolymer, as olefin polymers.

Further, examples of the base polymer include polyurethane polymers suchas polyester polyurethane and polyether polyurethane; and styrenepolymers such as styrene-ethylene-butylene copolymer (SEB),styrene-butadiene-styrene copolymer (SBS), hydrogenated products of SBS(styrene-ethylene-butylene-styrene copolymer (SEES)),styrene-isoprene-styrene copolymer (SIS), hydrogenated products of SIS(styrene-ethylene-propylene-styrene copolymer (SEPS)),styrene-isobutylene-styrene copolymer (SIBS),styrene-butadiene-styrene-butadiene copolymer (SBSB),styrene-butadiene-styrene-butadiene-styrene copolymer (SBSBS),polystyrene, acrylonitrile styrene resin (AS resin), and acrylonitrilebutadiene styrene resin (ABS resin), as polymers other than the olefinpolymers.

Further, examples of polymers that can be employed as the base polymerin this embodiment include fluorine polymers such as fluororesin andfluororubber; polyamide polymers such as polyamide resins, e.g.,polyamide 6, polyamide 11, polyamide 12, polyamide 6,6, and polyamide610, and polyamide elastomer; polyester resins such as polyethyleneterephthalate and polybutylene terephthalate; polyvinyl chloride resins;acrylic resins such as polymethylmethacrylate; silicone elastomers;butadiene rubber (BR); isoprene rubber (IR); chloroprene (CR); naturalrubber (NR); styrene butadiene rubber (SBR); acrylonitrile butadienerubber (NBR); and butyl rubber (IIR).

Among these, polyethylene is preferably used as the base polymer, inthat the physical properties can be easily adjusted by the crosslinkingdensity or the like, a decrease in physical properties due to hydrolysisis not much concerned, and the light weight of the resin itself isadvantageous for reducing the weight of the polymer foam. In particular,linear low density polyethylene (LLDPE) in which ethylene monomersserving as the main component are polymerized with a-olefins such as1-butene, 1-hexene, and 1-octene in the presence of a catalyst by amedium-to-low pressure method is suitable as the base polymer. Moreover,LLDPE in which ethylene and 1-hexene are polymerized using a single-sitecatalyst such as a metallocene catalyst is suitable as the base polymerbecause it has excellent impact resistance due to having crystals withuniform size, small lamellar, and large tie molecules, as compared toLLDPE polymerized using a multi-site catalyst such as a Ziegler-Nattacatalyst.

The fibers constituting the polymer foam together with such a basepolymer preferably has a length equal to or greater than the averagediameter of air bubbles in a polymer foam that is generally used forshoe sole members, in order to improve the compression set properties ofthe polymer foam. Further, it is preferable that, in the polymer foam ofthis embodiment, most part of the fibers is present in spaces inside theair bubbles, and only a part of the fibers is embedded within the bubblemembranes defining the air bubbles. The ratio of the embedded part withrespect to the length of the fibers is preferably not more than half,more preferably not more than 20%. Specifically, the fibers preferablyhave an average length equal to or greater than the average diameter ofthe air bubbles in the polymer foam, and the average length ispreferably at least 500 μm. The average length of the fibers ispreferably not more than 10 mm, more preferably not more than 8 mm,particularly preferably not more than 6 mm.

Further, the average diameter of the fibers is preferably not more than200 μm, more preferably not more than 100 μm, particularly preferablynot more than 20 μm, since the fibers having smaller average diameter(diameter) can exert more significant effects of the present invention.However, excessively small average diameter of the fibers may possiblycause difficulty in dispersion of the fibers in the polymer foam andmolding of the polymer foam. Therefore, the average diameter of thefibers is preferably at least 0.5 μm. The “average length” and “averagediameter” of the fibers can be determined by observing the fibers in thepolymer foam by an optical microscope, an electronic microscope, ortransmission observation, for example, using X-ray, determining by theobservation the length and diameter of a plurality (for example, aboutseveral tens) of fibers selected at random, and calculating averagevalues of the length and diameter.

In this embodiment, even if excellent compression set properties areimparted to the polymer foam by introducing the fibers, when the reboundresilience of the polymer foam is increased simultaneously therewith,the comfort when using shoes may possibly be insufficient.

Accordingly, the fibers are preferably dispersed in the polymer foamwithin the range that does not affect the hardness or the like, and thefibers are preferably dispersed so that the following conditionalexpression (1) is satisfied:

Hc1:S(1.1×Hco)  (1),

where “Hc1” denotes the Asker C hardness of the aforementioned polymerfoam, and “Hco” denotes the Asker C hardness of a polymer foam formed tohave the same specific gravity as the aforementioned polymer foam usingthe same polymer composition as the aforementioned polymer foam but notcontaining the fibers.

In order to prevent an increase in values of rebound resilience andhardness of the polymer foam as compared to the case of not containingthe fibers, the ratio of fibers with respect to the polymer foam ispreferably not more than 10 mass %, more preferably not more than 6 mass%, particularly preferably not more than 1 mass %. Further, in order toimpart excellent compression set properties to the polymer foam, theratio of fibers with respect to the polymer foam is preferably at least0.1 mass %, particularly preferably at least 0.5 mass %.

The fibers can serve as foreign matter to the base polymer when thepolymer foam is formed by foaming the polymer composition. Further,during foaming the polymer foam, in which bubble membranes composed ofthe polymer composition are stretched so that air bubbles grow, thefibers act to prevent formation of bubble membranes in theircircumferences. As a result, the fibers are enclosed in air bubbles thatare larger than their circumferences after the completion of thefoaming. That is, the polymer foam of this embodiment has air bubblesinside which the fibers are present (hereinafter, referred to as“fiber-containing bubbles”) and air bubbles inside which the fibers arenot present (hereinafter, “fiber non-containing bubbles”). Thefiber-containing bubbles are formed to be relatively larger in size ascompared to the fiber non-containing bubbles. Further, a fiber is notentirely incorporated inside the space of an air bubble generally at thetime of the completion of the foaming, and the fiber has both ends or amiddle part in the length direction embedded in a bubble membrane, orabutting the bubble membrane from the inside. That is, the fiber ispresent inside a coarse bubble, for example, as a rod supporting thebubble membrane defining the coarse bubble from the inside.

The presence of the fiber-containing bubbles and the fibernon-containing bubbles can be confirmed by observing a cross section ofthe polymer foam, for example, using a scanning electron microscope(SEM). Further, the size relationship between the fiber-containingbubbles and the fiber non-containing bubbles also can be confirmed byobserving the cross section of the polymer foam using the SEM. Theconfirmation can be made by selecting respective pluralities of bubblesat random from the fiber-containing bubbles and the fiber non-containingbubbles to be observed using the SEM, and comparing the average valuesof the cross sectional area of the selected pluralities (such as twenty)of air bubbles to each other. In this regard, a description is givenwith reference to FIG. 2. FIG. 2 is an SEM image of a similar product ofthe polymer foam No. 14 in EXAMPLES. It can be seen from the SEM imagethat the polymer foam includes coarse air bubbles inside thereof.Further, it can be seen from the SEM image that the polymer foam hasfiber-containing bubbles, since fibers are present inside two coarse airbubbles laterally aligned at the center of the image and a coarse airbubble located above the air bubble on the left side of theaforementioned two air bubbles. Although the description is not repeatedbelow, it has been confirmed by the SEM observation that air bubbles areformed also in polymer foams other than this polymer foam, in the samemanner as in FIG. 2, by dispersing fibers therein.

As described above, in the polymer foam of this embodiment, thefiber-containing bubbles that are coarse bubbles and the fibernon-containing bubble that are microbubbles coexist. Further, thepolymer foam of this embodiment not only simply contains the fibers soas to utilize the recovery force against the bending of the fibers orthe like for reducing the compression set, but also exhibits goodrecovering properties from the compressive strain by allowing the fibersto be present within relatively large air bubbles as compared to thefiber non-containing bubbles.

Although the function of the coarse bubbles associated with the effectof preventing the compression set in this regard is not sufficientlyclear, assuming that the coarse bubbles and the microbubbles have acommon deformation ratio (%) due to the compressive force, the coarsebubbles have a larger deformation amount (μm). In the case where thedeformation amount due to the compressive force of the coarse bubbles islarger than that of the microbubbles, the coarse bubbles are required,of course, to deform more largely than the microbubbles in order torecover the original shape when the compressive force is removed. Thefibers present inside the coarse bubbles are thought to be effectivelyused at this time for recovering the shape. That is, the fibers presentinside the coarse bubbles undergo elastic deformation in the bendingdirection when the compressive force is applied, whereas they exert arecovery force to return to the original shape when the compressiveforce is removed. Therefore, the force exerted by the fibers themselveswhen recovering the shape can be utilized for recovering the shape ofthe coarse bubbles. It is thought that the polymer foam of thisembodiment exerts excellent recovering properties from the compressivestrain by such a reason as compared to a polymer foam simply containingthe fibers.

In order to exert such effects more significantly, the followingconditional expression (2) is preferably satisfied, and the followingconditional expression (3) is more preferably satisfied, when theflexural modulus of the fibers at least at room temperature (25° C.) isexpressed as E₁ (MPa), and the flexural modulus of the polymercomposition forming bubble membranes of the fiber-containing bubble atroom temperature (25° C.) is expressed as E₂ (MPa):

E ₁ >E ₂  (2), and

E ₁≥(2×E ₂)  (3).

It is preferable that the relationship represented by the aforementionedconditional expressions (2) and (3) be satisfied not only at roomtemperature but also at all times in a normal operating temperaturerange expected for the shoe sole members. That is, the flexural modulusof the fibers is preferably always larger, particularly preferably atleast twice larger, than the flexural modulus of the polymercomposition, for example, in the range of 0° C. to 50° C.

Specific examples of the fibers that are preferably dispersed in thepolymer foam include inorganic fibers such as carbon fibers, glassfibers, and rock wool, and organic fibers such as synthetic fibers,natural fibers, and regenerated fibers. Among these, the fibers arepreferably organic fibers in that breakage is unlikely to occur duringdeformation such as bending, and the properties to exert a recoveryforce from the deformation such as bending are relatively excellent.Further, the organic fibers are preferable also in that they generallyhave a low specific gravity as compared to the inorganic fibers.

In the case where synthetic fibers are employed as the organic fibers,aliphatic polyamide fibers such as polyamide 6, polyamide 6,6, polyamide11, and polyamide 12; aromatic polyamide fibers such as poly-p-phenyleneterephthalamide fibers and poly-m-phenyleneisophthalamide fibers;polyolefin fibers such as polyethylene fibers and polypropylene fibers;polyester fibers such as polyethylene terephthalate fibers, polybutyleneterephthalate fibers, polyethylene naphthalate fibers, polybutylenenaphthalate fibers, polylactic acid fibers, and polyarylate fibers;polyphenylene sulfide fibers; polyurethane fibers; acrylic fibers; poly(p-phenylene benzobisoxazole) fibers; polyimide fibers; polyvinylalcohol fibers; or fluororesin fibers, for example, can be employed.

In the case where natural fibers are employed as the organic fibers,cotton, hemp, silk, or wool, for example, can be employed. In the casewhere regenerated fibers are employed as the organic fibers, cellulosefibers, or acetate fibers and rayon fibers that are obtained bychemically treating the cellulose fibers can be employed.

Among these, aromatic polyamide fibers, polyolefin fibers, polyesterfibers, polyphenylene sulfide fibers, polyurethane fibers, acrylicfibers, poly (p-phenylene benzobisoxazole) fibers, polyimide fibers,polyvinyl alcohol fibers, cellulose fibers, and fluororesin fibers aresuitable in that their recovery force from the deformation such asbending is excellent.

In the case where the base polymer is polyethylene such as LLDPE, fibersmade of a material having low affinity to the base polymer, such asaromatic polyamide fibers and polyphenylene sulfide fibers are employed,thereby allowing the fiber-containing bubbles to be larger in size thanthe fiber non-containingbubbles more reliably. Further, in the casewhere the base polymer of the polymer foam is LLDPE, fibers made of amaterial having a higher flexural modulus than the base polymer, such asthe aromatic polyamide fibers and the polyphenylene sulfide fibers areemployed, thereby allowing the compression set properties of the polymerfoam to be further excellent.

It should be noted that, even if such fibers having significant effectsare employed, for example, in the case where the fibers are aligned inthe thickness direction of the shoe sole members, the comfort of shoesmay possibly be impaired due to a significant increase in reboundresilience (hardness improvement) following the effect of improving thecompression set properties. Accordingly, the fibers are preferablydispersed in the polymer foam at random without orientation.

The polymer composition for forming the polymer foam, for example, cancontain a crosslinking agent for crosslinking the base polymer. Examplesof the crosslinking agent include organic peroxides, maleimidecrosslinking agents, sulfur, phenolic crosslinking agents, oximes, andpolyamines. Among these, organic peroxides are preferable.

Examples of the organic peroxides include dicumyl peroxide, di-t-butylperoxide, 2,5-dimethyl-2,5-di-(t-butylperoxy) hexane,2,5-dimethyl-2,5-di-(t-butylperoxy) hexyne-3, 1,3-bis(t-butylperoxyisopropyl) benzene, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, n-butyl-4,4-bis(t-butylperoxy) valerate, benzoyl peroxide, p-chlorobenzoyl peroxide,2,4-dichlorobenzoyl peroxide, t-butylperoxybenzoate,t-butylperoxyisopropyl carbonate, diacetyl peroxide, lauroyl peroxide,and t-butyl cumyl peroxide.

Further, the crosslink density of the polymer foam can be adjusted byallowing the polymer composition to contain a crosslinking aid togetherwith the crosslinking agent. Examples of the crosslinking aid includedivinyl benzene, trimethylolpropanetrimethacrylate, 1,6-hexanediolmethacrylate, 1,9-nonanediol dimethacrylate, 1,10-decanedioldimethacrylate, trimellitic acid triallyl ester, triallyl isocyanate,neopentyl glycol dimethacrylate, 1,2,4-benzene tricarboxylic acidtriallyl ester, tricyclodecane dimethacrylate, and polyethylene glycoldiacrylate.

Examples of a foaming agent for foaming the polymer foam include azocompounds such as azodicarbonamide (ADCA), 1,1′-azobis(1-acetoxy-1-phenylethane), dimethyl-2,2′-azobisbutyrate,dimethyl-2,2′-azobisisobutyrate, 2,2′-azobis (2,4,4-trimethylpentane),1,1′-azobis (cyclohexane-1-carbonitrile), and 2,2′-azobis[N-(2-carboxyethyl)-2-methyl-propionamidine]; nitroso compounds such asN,N′-dinitrosopentamethylenetetramine (DPT); hydrazine derivatives suchas 4,4′-oxybis (benzenesulfonyl hydrazide), anddiphenylsulfone-3,3′-disulfonyl hydrazide; semicarbazide compounds suchas p-toluenesulfonyl semicarbazide; and thermally decomposable organicfoaming agents such as trihydrazino triazine.

Further, examples of the foaming agent that can be employed includebicarbonates such as sodium hydrogen carbonate and ammonium hydrogencarbonate; carbonates such as sodium carbonate and ammonium carbonate;nitrites such as ammonium nitrite; and thermally decomposable inorganicfoaming agents such as hydrogen compounds.

Further, organic foaming agents such as various aliphatic hydrocarbons,e.g., methanol, ethanol, propane, butane, pentane, and hexane, andinorganic foaming agents such as air, carbon dioxide, nitrogen, argon,and water also can be used as the foaming agent when forming the polymerfoam.

Examples of other additives to be contained in the polymer compositioninclude a dispersant, a processing aid, a weathering agent, a flameretardant, a pigment, a mold release agent, an antistatic agent, anantibacterial agent, and a deodorizer.

The method for forming the polymer foam using such a polymer compositionis not specifically limited, and a conventionally known method can beemployed therefor. It should be noted that an example of the shoe solemember of the present invention is described as above in thisembodiment. However, the shoe sole member of the present invention isnot limited to the aforementioned example. For example, the shoe solemember of the present invention may be formed using only the polymerfoam described above, or may be formed using other materials such asfabrics and resin sheets in combination, within the range in which theaforementioned effects such as excellent recovering properties fromcompressive deformation are not significantly impaired. Further,conventionally known technical matters may be employed in the shoe solemember of the present invention, within the range in which the effectsof the present invention are not significantly impaired, even if thematters are not specifically described above.

EXAMPLES

Next, the present invention is described further in detail by way ofexamples. However, the present invention is not limited to theseexamples.

The compound materials used for examinations are shown below.

LLDPE 1

Linear low density polyethylene (comonomer: 1-hexene,metallocene-catalyzed polymerization product), product name “Evolue SP1540”, manufactured by Prime Polymer Co., Ltd., with a flexural modulusof about 150 MPa

EVA1

Ethylene-vinyl acetate copolymer (VA 10%), product name “Ultrasen 540”,manufactured by TOSOH CORPORATION, with a flexural modulus of about 95MPa

ARM 1

Aromatic polyamide fibers, with an average length of 200 μm, an averagediameter of 20 μm, and a flexural modulus of about 62 GPa

ARM 2

Aromatic polyamide fibers, with an average length of 500 μm, an averagediameter of 20 μm, and a flexural modulus of about 62 GPa

ARM 3

Aromatic polyamide fibers, with an average length of 1000 μm, an averagediameter of 20 μm, and a flexural modulus of about 62 GPa

PPS 1

Polyphenylene sulfide fibers, with an average length of 6000 μm, anaverage diameter of 10 μm, and a flexural modulus of about 3 GPa

GF 1

Glass fibers, with an average length of 3000 μm, an average diameter of20 μm, and a flexural modulus of about 72 GPa

CF 1

Carbon fibers, with an average length of 3000 μm, an average diameter of20 μm, and a flexural modulus of about 220 GPa

PAR1

Polyarylate fibers, with an average length of 3000 μm, an averagediameter of 20 μm, and a flexural modulus of about 180 GPa

PET1

Polyethylene terephthalate fibers, with an average length of 3000 μm, anaverage diameter of 10 μm, and a flexural modulus of about 14 GPa

Other Additives

Stearic acid, zinc oxide, a foaming agent (azodicarbonamide, “AC#3C-K2”,manufactured by EIWA CHEMICAL IND. CO., LTD.), a crosslinking agent(dicumyl peroxide, “PERCUMYL D”, manufactured by NOF CORPORATION), and acrosslinking aid (triallyl isocyanurate)

Production and Evaluation of Polymer Foam

The aforementioned compound materials were mixed at ratios shown inTables 1 to 4 below, and polymer foams having specific gravities shownin Tables 1 to 4 below were produced. Tables 1 to 4 also showmeasurement results of the Asker C hardness and compression set of thepolymer foams.

It should be noted that the values of the flexural modulus of LLDPE 1,EVA 1, and the fibers are estimated values. More specifically, thevalues of the flexural modulus of LLDPE 1 and EVA 1 are estimated asequivalent values of the tensile elastic modulus, and the measuredvalues of the tensile elastic modulus are shown. Further, literaturevalues are shown as the values of the flexural modulus of the fibers.The tensile elastic modulus of LLDPE 1 and EVA 1 is values of thestorage elastic modulus of strip-shaped samples measured in accordancewith JIS K 7244-4. Those values are calculated by measuring the dynamicviscoelasticity under the following conditions.

Conditions for Measuring Tensile Elastic Modulus

Measurement device: Dynamic viscoelasticity measuring instrument,Rheogel-E4000, manufactured by UBM Co., Ltd.

Sample shape: Strip shape with a length of 33±3 mm, a width of 5±0.3 mm,and a thickness of 2±0.3 mm

Measurement mode: Tensile mode of sine wave distortion

Distance between chucks: 20±0.2 mm

Temperature: 23° C.

Frequency: 10 Hz

Dynamic strain: 3 to 5 μm

Estimated values of the flexural modulus of the fibers and the basepolymer are shown above. However, there is a difference of two or moredigits between them. Therefore, even if the estimated values aredifferent from actual values to some extent, it is highly probable thatthe following condition is satisfied in the polymer foams shown inTables 1 to 4 below, when the flexural modulus of the fibers at 25° C.is expressed as E₁ (MPa), and the flexural modulus of polymercompositions forming bubble membranes in the polymer foams at 25° C. isexpressed as E₂ (MPa):

E ₁≥(2×E ₂).

TABLE 1 Polymer foam No. 1 No. 2 No. 3 No. 4 No. 5 No. 6 LLDPE 1 (Partsby mass) 100 100 100 100 100 100 Fibers (Parts by mass) None None NoneNone None None Stearic acid 1 1 1 1 1 1 Zinc oxide 0.5 0.5 0.5 0.5 0.50.5 Foaming agent 6 8 10 4 6 8 Crosslinking agent 1 1 1 0.7 0.7 0.7Crosslinking aid 0.3 0.3 0.3 0.3 0.3 0.3 Fiber content (mass %) 0 0 0 00 0 Asker C hardness (JIS K7312) 62 48 40 65 52 40 Specific gravity (JISK7112) 0.117 0.078 0.058 0.140 0.091 0.062 Compression set(ASTMD395A)[%] 16 31 63 14 20 52

TABLE 2 Polymer foam No. 7 No. 8 No. 9 No. 10 No. 11 No. 12 No. 13 No.14 No. 15 No. 16 LLDPE 1 100 100 100 100 100 100 100 100 100 100 (Partsby mass) Fibers ARM 1 1.4 7.2 (Parts (200 μm) by ARM 2 2.8 7.2 mass)(500 pm) ARM 3 0.72 0.72 0.72 0.72 (1000 μm) PPS 1 0.67 0.67 (6000 μm)Stearic acid 1 1 1 1 1 1 1 1 1 1 Zinc oxide 0.5 0.5 0.5 0.5 0.5 0.5 0.50.5 0.5 0.5 Foaming agent 5 6 7 8 5 6 7 8 6 7 Crosslinking agent 0.7 10.7 1 0.7 1 0.7 1 0.7 0.7 Crosslinking aid 0.3 0.3 0.3 0.3 0.3 0.3 0.30.3 0.3 0.3 Fiber content 1.3 5.8 2.4 5.8 0.7 0.7 0.6 0.6 0.6 0.6 (mass%) Asker C hardness 45 44 46 50 54 58 35 47 52 45 (JIS K7312) Specificgravity 0.080 0.077 0.081 0.086 0.110 0.117 0.061 0.081 0.093 0.080 (JISK7112) Compression set 25 26 18 12 12 10 35 15 14 20 (ASTMD395A) [%]

TABLE 3 Polymer foam No. 17 No. 18 No. 19 No. 20 No. 21 No. 22 No. 23No. 24 No. 25 LLDPE 1 100 100 100 100 100 100 100 100 100 (Parts bymass) Fibers GF 1 2.5 (Parts by (3000 μm) mass) CF 1 0.88 1.76 4.4 8.817.6 (3000 μm) PET 1 0.7 1.4 (3000 μm) PAR 1 0.7 (3000 μm) Stearic acid1 1 1 1 1 1 1 1 1 Zinc oxide 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 Foamingagent 9 7 7 7 7 7 7 7 7 Crosslinking agent 1 0.7 0.7 0.7 0.7 0.7 0.7 0.70.7 Crosslinking aid 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 Fiber content2.1 0.8 1.6 3.7 6.9 12.2 0.6 1.2 0.6 (mass %) Asker C hardness 46 49 5051 55 56 41 40 40 (JIS K7312) Specific gravity 0.076 0.083 0.081 0.0870.093 0.104 0.064 0.060 0.061 (JIS K7112) Compression set 25 22 22 18 1614 36 43 31 (ASTMD395A) [%]

TABLE 4 Polymer foam No. 26 No. 27 No. 28 No. 29 No. 30 No. 31 EVA1(Parts by mass) 100 100 100 100 100 100 Fibers (Parts ARM 1 2.5 2.5 2.5by mass) (200 μm) Stearic acid 1 1 1 1 1 1 Zinc oxide 0.5 0.5 0.5 0.50.5 0.5 Foaming agent 2 3 4 2 3 4 Crosslinking agent 0.6 0.6 0.6 0.6 0.60.6 Fiber content (mass %) 0 0 0 1.3 1.3 1.3 Asker C hardness (JISK7312) 62 50 40 61 45 38 Specific gravity (JIS K7112) 0.17 0.114 0.0870.169 0.116 0.091 Compression set (ASTMD395A)[%] 14 29 41 13 17 30

In the results shown above, for example, as compared to the compressionset (16%) of the polymer foam No. 1 having a specific gravity of 0.117and not containing fibers, the compression set (10%) of the polymer foamNo. 12 having a similar specific gravity is significantly improved. Asimilar improvement effect can be seen between the polymer foams No. 2and No. 8. Further, the effect of the present invention can be seen alsoin the cases (No. 26 to No. 31) where the polymer foams are formed usingbase polymers other than the base polymer of the polymer foam No. 1 orthe like. That is, it is understood that the present invention canprovide a shoe sole member exhibiting excellent recovering propertiesfrom compressive deformation applied during use.

REFERENCE SIGNS LIST

-   -   1: Shoe    -   3: Midsole    -   4: Outer sole

1. A shoe sole member comprising a polymer foam that partially orentirely forms the shoe sole member and fibers being dispersed at randomwithout orientation in the polymer foam.
 2. The sole according to claim1, wherein the fibers are organic fibers.
 3. The shoe sole memberaccording to claim 2, wherein the organic fibers are one kind selectedfrom aromatic polyamide fibers, polyolefin fibers, polyester fibers,polyphenylene sulfide fibers, polyurethane fibers, acrylic fibers, poly(p-phenylene benzobisoxazole) fibers, polyimide fibers, polyvinylalcohol fibers, cellulose fibers, and fluororesin fibers.
 4. The shoesole member according to claim 1, wherein the polymer foam includesfiber-containing bubbles inside which the fibers are present and fibernon-containing bubbles inside which the fibers are not present, and thefiber-containing bubbles are larger in size than the fibernon-containing bubbles.
 5. The shoe sole member according to claim 1,wherein when a flexural modulus of the fibers at 25° C. is expressed asE₁ (MPa), and a flexural modulus of a composition of the polymer foamforming bubble membranes of the fiber-containing bubbles at 25° C. isexpressed as E₂ (MPa), the following condition is satisfied:E ₁≥(2×E ₂).
 6. The shoe sole member according to claim 1, wherein thefibers have an average length of at least 500 μm.
 7. The shoe solemember according to claim 1, wherein the fibers have an average diameterof at least 0.5 μm and not more than 200 μm.
 8. The shoe sole memberaccording to claim 1, wherein the polymer foam has a specific gravity ofat least 0.01 and not more than 0.15, and the fibers are dispersed inthe polymer foam so that the following condition is satisfied:H _(c1)≤(1.1×H _(c0)), where “H_(c1)” denotes an Asker C hardness of theforegoing polymer foam, and “H_(c0)” denotes an Asker C hardness of apolymer foam formed to have the same specific gravity as the foregoingpolymer foam using the same composition as the foregoing polymer foambut not containing the fibers.
 9. A shoe sole member comprising apolymer foam that partially or entirely forms the shoe sole member andfibers, and having a compression set characteristic of at least 1 to 40%based on method A of ASTM D
 395. 10. The shoe sole member according toclaim 9, wherein the fibers are organic fibers.
 11. The shoe sole memberaccording to claim 10, wherein the organic fibers are one kind selectedfrom aromatic polyamide fibers, polyolefin fibers, polyester fibers,polyphenylene sulfide fibers, polyurethane fibers, acrylic fibers, poly(p-phenylene benzobisoxazole) fibers, polyimide fibers, polyvinylalcohol fibers, cellulose fibers, and fluororesin fibers.
 12. The shoesole member according to claim 9, wherein the polymer foam includesfiber-containing bubbles inside which the fibers are present and fibernon-containing bubbles inside which the fibers are not present, and thefiber-containing bubbles are larger in size than the fibernon-containing bubbles.
 13. The shoe sole member according to claim 9,wherein when a flexural modulus of the fibers at 25° C. is expressed asE₁ (MPa), and a flexural modulus of a composition of the polymer foamforming bubble membranes of the fiber-containing bubbles at 25° C. isexpressed as E₂ (MPa), the following condition is satisfied:E ₁≥(2×E ₂).
 14. The shoe sole member according to claim 9, wherein thefibers have an average length of at least 500 μm.
 15. The shoe solemember according to claim 9, wherein the fibers have an average diameterof at least 0.5 μm and not more than 200 μm.
 16. The shoe sole memberaccording to claim 9, wherein the polymer foam has a specific gravity ofat least 0.01 and not more than 0.15, and the fibers are dispersed inthe polymer foam so that the following condition is satisfied:H _(c1)≤(1.1×H _(c0)), where “H_(c1)” denotes an Asker C hardness of theforegoing polymer foam, and “H_(c0)” denotes an Asker C hardness of apolymer foam formed to have the same specific gravity as the foregoingpolymer foam using the same composition as the foregoing polymer foambut not containing the fibers.